Lower limb loss is a growing clinical problem in our society and individuals with limb loss face significant morbidity related to walking with a prosthetic limb. Research aimed at optimizing prosthetic prescription is vital in order to minimize functional disability in this population. There is a wide selection of prosthetic feet available today that possess a variety of stiffness characteristics each providing different shock absorbing capacity and rate of energy release. When prescribing a prosthetic foot for an individual with limb loss, the clinician must determine which foot will have stiffness characteristics optimally suited for that individual's particular set of functional abilities and goals. Improving the ability to optimize prosthetic foot stiffness to better match the functional abilities and goals of each individual would greatly enhance the clinical practice of lower limb prosthetics and therefore enhance the function of individuals with lower limb loss. Therefore the primary objective of this research is to determine what combination of hindfoot and forefoot stiffness profiles provides optimal function according to the performance needs of individuals with lower limb loss. To meet this objective, we plan to: - Determine the effects of individual hindfoot and forefoot component stiffness on the effective stiffness of the prosthetic foot, using a robotic gait simulator - Determine the effects of a functional range of prosthetic foot stiffness profiles on impact forces and rate of loading during level walking, lower limb kinematics and kinetics, and energy consumption in transtibial amputee subjects - Determine how prosthetic foot geometry interacts with stiffness to provide shock absorption and optimal foot rollover - Determine which subsets of prosthetic foot stiffness profiles are biomechanically optimal for task-specific goals including upright standing balance, gait initiation and termination, and level walking at different speeds In support of these objectives and aims, we have cultivated a previously established collaboration between the VA RR&D Center of Excellence for Limb Loss Prevention and Prosthetic Engineering at the VA Puget Sound Health Care System and the Human Biomechanics and Control Laboratory at the University of Michigan to design and prototype a novel multi- component prosthetic foot. The innovative design of this new foot can be configured in a myriad of combinations made of different component stiffness levels, positions and orientations to allow direct examination of the effect of these changes on the overall stiffness profile of the prosthetic foot throughout the stance phase of gait. Additional components can be readily produced to change structural features, including the presence or absence of keel overlap, solid or split toes and heels, rotational axes at the ankle, and the use of foam or rubber cushioning above or below the keels. The results of this research project will directly benefit the portion of the general population that has experienced lower limb loss, and inform future innovations in prosthetic foot development. PUBLIC HEALTH RELEVANCE: It has been estimated that over 100,000 lower extremity amputations occur annually in the United States, due to trauma or vascular complications. The results of this research project will directly benefit the portion of the general population that has experienced lower limb loss, and inform future innovations in prosthetic foot development. The population of individuals with lower limb loss within the VA system is growing every year. With the increasing incidence of diabetes mellitus, there will likely be a proportional increase in lower extremity amputations secondary to complications of the disease process as well. The VA System currently serves approximately 5,000 new individuals with limb loss each year in addition to the tens of thousands that continue to be cared for. Veterans are expected to benefit greatly from an increased understanding of the prosthetic stiffness profile continuum.